Overheating on new build

[polecat]

Hey fellas, I need some help with my overheating problem. After getting it all back together I was able to get it started and break the cam in. As soon as I took it for a road test, a couple of days later, it overheated on me not long after hitting the main road. I have talked to a few guys here and the consensus is some air locked in the cooling system somewhere. You guys have any ideas for purging the air out. I have already pulled the therm. and boiled it, and then boiled a new one and they both opened about the same temp. 180 deg. therm. I have the heater core bypassed right now, but that is the only thing out of the ordinary I have done compared to the old build. I would appreciate any help.

johnny

 

[broncnaz]

How your radiater is it old, new unknown ? over time the cores get clogged up it may be time to get it rodded out or put in a new radiater. You may also want to replace the radiater cap it may not be holding pressure. other than that about the only other things are check your timing make sure its not to far advanced and check your jetting make sure its not to lean. What size(overbore) of pistons did you put in .040 is about the max anything larger usually causes the engine to run a bit warmer although it shouldnt be overheating if all the other factors are in good condition.

 

[wildbill]

;D ;D ;D You can burp the cooling by taking the heater hose off the top of the intake and add water till it runs out of the L and then put the hose back on and you should be good to go. Do this cold good luck. also a new motor will run a little hotter than a used one. %) %) %) Bill %)

 

[74bronc]

I know people automatically suspect air bubbles in the cooling system when an overheating problem comes up, but I honestly have never had one in a 289/302/351W. First, "overheating" means different things to different people. What does your temperature guage read? Do you have an aftermarket guage on the engine or are you relying on the stock guage? Does it actually get so hot that it boils over? A new engine will always run 10-15 degrees warmer when it is new and the temp will stabilize after it has been well broken in. My 351W took well over 3K for the engine temp to come down to a consistent temp.

If we are talking 210-215 degrees or so, that isn't too much to worry about as long as it doesn't go higher. if we are up in the 225 range, I would be worried.

One big problem on new rebuilds is the head gasket placement. Did you build the motor or did you have it done? It is easy to put the head gaskets on backwards which will block some coolant ports. Just a thought that always comes up when a new engine has heating problems.

 

[pinenuts]

I just fired up my rebuilt 302 and had the same problem. What I noticed was that the heater hoses were quite hot, but the radiator hoses wern't. I suspected the thermostat, but every time I started it up and let it cool off I could add coolant. After doing this about four times it started cooling properly. I guess I just had to much air in the system for the water pump to work.

 

[JWMcCrary]

I have had experience with the head gasket being on backwards. If this is the case it will build up a lot of pressure, the top radiator hose will swell up and become extremely tight. When I had this problem it would idle for a long time and not over heat, but drive down the road about a mile and back and it was HOT...very HOT.

 

[rcmbronc]

You may also want to make sure that the valves are set correctly. If they are set too tight, the motor will also have a tendency to overheat.

 

[Mr Joe]

I have had experience with the head gasket being on backwards. If this is the case it will build up a lot of pressure, the top radiator hose will swell up and become extremely tight. When I had this problem it would idle for a long time and not over heat, but drive down the road about a mile and back and it was HOT...very HOT.

I have seen this too... Also, did you have the block bored and if so, how much?

 

[polecat]

Thanks for the replys. The radiator is freshly flushed out. The water pump is new. The block was bored 30 over. The top hose does seem to get tight, but I don't know what is too tight. The temp runs around 210-230 just setting idleing. As soon as I hit the road the temp. skyrockets. I was told that if you look at the front of the head down by the exhaust ports where the head meets the block you should be able to read " front " on the head gasket? Can any of you guys confirm this. I just looked at mine tonight, and I could not make out any letters or front on the gasket. Thanks again for the help.

johnny

 

[JWMcCrary]

Yes...they should have front marked on them. The gaskets are the same, so on one side the word front is usually face down on the block, the other faces the head. The best way to tell is the water jacket openings should be at the back, the front openings get covered up with the gasket. I am hoping memory serves me right on this..but I am pretty sure this is right.

 

[76Broncofromhell]

The thing usually runs hot as the rings set into the block. You have to remember that everything is extremely tight on a new motor. My 351's and 302's usually run hot for a few hundred miles after initial fire-up. If you have Moly rings it will last a little longer, but usually that means 205 at freeway speeds where the temperature should be the coolest.

Since your heating problem is at speed with lots of airflow through the radiator, I would also check:
-the fan is on the right way,
-correct rotation waterpump
-check your base timing (no more than 14 degrees)
-check the mixture and for vacuum leaks
-the lower radiator hose to make sure it isn't crushing under RPM